Here's my understanding of it, I trust someone will correct me if I'm wrong.
The obvious pro of IPv6 is more address space, supposedly enough so that almost every device can have its own public IP address, although that probably won't happen. The obvious con is that it's incompatible with IPv4. Eventually (hopefully) everyone will get switched and it won't be a problem.
In all likelihood, you can't sell your IP address because you don't 'own' it, your ISP does. They actually have a pool of IPs that they let their customers use when they connect. They can sell addresses out of their pool, but only to people who have contacted ARIN (the people responsible for giving out IPs in North America) and been turned down.
It's hard to say exactly what will happen when IPv4 addresses run out. Perhaps they'll just start giving out IPv6 addresses, which would result in a small number of people being completely unable to connect (those people still using old systems that don't support IPv6), on top of that, attempts at accessing IPv4 resources from an IPv6 address would have to go through a sort of gateway, which would probably be laggy and break certain protocols. Not so bad, and I imagine that public resources on the Internet would get an IPv6 pretty quick (lots of sites already have one, like Google and Facebook). Of course, it could end up with all of America looking like Raccoon City for all I know.
As far as privacy goes, IPv6 will be worse
than IPv4 since you're supposed
to use your MAC address as the last part of your IP address, but there's nothing forcing you to do this. There are other security flaws too, I'm sure, but it looks like, for the most part, the only difference will be the longer address.
Another DEFCON lecture with some useful information - http://www.youtube.com/watch?v=2clTKh2vFAE